This application relates to a flame-retarded polyphenylene ether (PPE) compositions and to a method of making same.
PPE is a thermoplastic material with high glass transition temperature, high dimensional stability, low specific gravity, hydrolytic stability and good mechanical performance. This combination of properties allows PPE based formulations to be injected molded into products which are used for high heat applications, for example in the automotive, electrical, and construction industries. For some applications, where increased modulus and strength are required, PPE may be reinforced with glass fibers. However, these reinforced PPE formulations have undesirable flammability characteristics. At high temperature or when exposed to flame, glass-filled PPE tends to burn continuously without extinguishing. Because of this, fire-retarded grades of glass-filled PPE (especially those rated UL94 V0) tend to be formulated using a large amount (for example  greater than 15% by weight for a rating of UL94 V0 at {fraction (1/16)}th inch thickness) of fire-retardant additives such as phosphorus-containing organic compounds. This increases the cost of the product, and also makes it more difficult to formulate glass fiber-reinforced PPE to meet UL94 V0 fire-retardant standards, because the addition of large amounts of phosphorus-containing organic compounds like resorcinol diphosphate plasticizes the composition and significantly reduces the heat deflection temperature of the formulation.
The present invention provides PPE compositions with good fire and flame-retardant characteristics, which utilize lower levels of organophosphate fire-retardant and which therefore do not suffer from the drawbacks of previously known fire- and flame-retardant PPE compositions. The compositions comprise
(a) a polymer component comprising at least 50% by weight of a polyphenylene ether;
(b) glass reinforcing fibers in an amount sufficient to increase the modulus and strength of the polymer component;
(c) a fire retardant component, preferably comprising an organophosphate fire retardant;
(d) an organoclay component in an amount effective to enhance the flame-retardant characteristics of the composition; and
(e) a mineral component. Other conventional additives utilized in formulation of PPE may be included. This composition can be used in the manufacture of injection molded articles such as electronic components, including television internals such as deflection yokes; printer chassis and plastic pallets.
The present invention further provides a method for preparation of a glass-reinforced PPE composition. In accordance with this method, the composition is prepared by compounding a mixture of
(a) a polymer component comprising at least 50% by weight of a polyphenylene ether;
(b) glass reinforcing fibers in an amount sufficient to increase the modulus and strength of the polyphenylene ether matrix;
(c) a fire retardant component, preferably comprising an organophosphate fire retardant;
(d) an organoclay component in an amount effective to enhance the flame-retardant characteristics of the composition; and
(e) a mineral component., as well as optional other components at elevated temperature to provide a homogenous blend of the materials. This compounding is suitably carried out in a screw type extruder at a temperature of 520 to 620xc2x0 F., preferably from 540 to 560xc2x0 F.
The PPE compositions of the present invention comprise a polymer component comprising at least 50% by weight of a polyphenylene ether; glass reinforcing fibers in an amount sufficient to increase the modulus and strength of the polyphenylene ether matrix; an organophosphate fire retardant component; an organoclay component in an amount effective to enhance the flame-retardant characteristics of the composition; and a mineral component. These components act synergistically to provide glass-fiber reinforced PPE with good fire and flame-retardant characteristics, which utilize lower levels of organophosphate fire-retardant and which therefore do not suffer from the drawbacks of previously known fire- and flame-retardant PPE compositions.
This synergism is demonstrated in the results of the tests described below in the Examples which are summarized in Tables 1, 3 and 4. In these tests, samples of glass-fiber reinforced PPE without organoclay and with various loadings of organoclay were prepared by compounding in a twin screw extruder. Some of the compositions were prepared with a mineral component (mica) and others without a mineral component. The samples were then injection molded and tested for flame-out time in accordance with the UL protocol for V0 rating.
The experiments indicated that addition of small amounts of organoclay along with a mineral component to fire-retardant glass-fiber reinforced PPE allowed achievement of enhanced fire-retardant performance and compliance with the UL94 V0 standard. Addition of larger amounts of organoclay, or the addition of small amounts of organoclay in the absence of the mineral component resulted in a deterioration of the fire-retardant performance. Thus, it is clear that there is a critical and synergistic combination of ingredients which leads to the improved characteristics of the compositions of the present invention.
The composition of the invention is made from a polymer component in which various fillers and additives are incorporated. As used herein, the term xe2x80x9cpolymer componentxe2x80x9d refers to the combined mass of all organic polymers present in the composition. While the polymer component may be 100% of a polyphenylene ether, it may also include other polymers selected to achieve desired properties in the final composition. Thus, the polymer component of the composition comprises at least 50% by weight of one or more species of polyphenylene ether. As used herein, the term xe2x80x9cpolyphenylene etherxe2x80x9d refers to individual polymeric PPE species or to mixtures of polymeric PPE species unless the context indicates otherwise.
PPE useful in the present invention is a polymer having repeat units of the general formula 
wherein in the formula, R1, R2, R3, and R4 which may be the same or different each represent a member selected from the group consisting of hydrogen atoms, halogen atoms, substituted and unsubstituted alkyl groups and substituted and unsubstituted alkoxy groups. The PPE may be a homopolymer, i.e. the repeat units have the same structural formula, or a copolymer consisting of a combination of two or more types of repeat units where at least one of the R1, R2, R3, and R4 are different for each different repeat unit comprising the copolymer. The polymer is terminated at each end by a monovalent chemical group or atom such as hydrogen, a halogen, a monovalent hydrocarbon radical (saturated, unsaturated or aromatic) or the like. There are no particular restrictions on the method of manufacturing PPE. For example, this may be produced by reacting phenols according to the procedures presented in the specifications of U.S. Pat. Nos. 3,306,874, 3,257,357, or 3,257,358. Examples of these phenols include 2,6-dimethylphenol, 2,6-diethylphenol, 2,6-dibutylphenol, 2,6-dilaurylphenol, 2,6-dipropylphenol, 2,6-diphenylphenol, 2-methyl-6-ethylphenol, 2-methyl-6-cyclohexylphenol, 2-methyl-6-tolyl)phenol, 2-methyl-6-methoxyphenol, 2-methyl-6-butylphenol, 2,6-dimethoxyphenol, 2,3,6-trimethylphenol, 2,3,5,6-tetramethylphenol, 2,6-diethoxyphenol, etc., but the invention is not limited to these. One may either use a corresponding homopolymer obtained by reacting one of the above substances or a corresponding copolymer obtained by reacting two or more of the above substances and having the different units contained in the above formula. Specific examples of PPE polymers useful in the invention include but are not limited to poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-diethyl-1,4-phenylene) ether, poly(2-methyl-6-ethyl-1,4-phenylene) ether, poly(2-methyl-6-propyl-1,4-phenylene) ether, poly(2,6-dipropyl-1,4-phenylene) ether, and poly(2-ethyl-6-propyl-1,4-phenylene) ether. Moreover, an example of the PPE copolymer is a copolymer partially containing an alkyl trisubstituted phenol such as 2,3,6-trimethylphenol in the aforementioned polyphenylene ether repeated unit. The PPE resins may also be copolymers having a styrene compound grafted on. An example of such a styrene-compound-grafted polyphenylene ether is a copolymer obtained by graft polymerization of a styrene compound such as styrene, .alpha.-methylstyrene, vinylstyrene, or chlorostyrene onto the aforementioned PPE.
Additional polymeric materials which may be included, individually or in combination, in the polymer component of the invention include crystalline polystyrene which can be added in amounts of 0 to 50% by weight of the polymer component to improve processability, high impact polystyrene (HIPS), which can be added in amounts of 0 to 50% by weight of the polymer component to improve processability and increase impact strength; EPDM and styrene-butadiene block copolymers which can be added in amounts of 0 to 20% by weight of the polymer component to improve the impact properties of the polymer component; and polyamides such as nylon-6,6 and nylon-6 which can be added in amounts of 0 to 50% by weight of the polymer component to improve melt flow and impart increased resistance to organic solvents. The polymeric component may also include a terpene phenol resin (i.e., a copolymer of monoterpenes and phenol such as NIREZ 2150/7042(trademark)) in amounts of 0 to 25% by weight of the polymeric component to provide better flow to the composition. Other polymers that can be blended in the compositions of the invention include polyphenylene sulfides in amounts from 0 to 50% by weight to improve heat deflection temperature and the flow.
Glass fibers suitable for use in the compositions of the invention may be of various lengths appropriate and thicknesses appropriate to the application. Coatings of coupling agents, such as aminosilanes may be employed if desired. The glass fibers are added in an amount sufficient to increase the modulus and the strength of the product by a desired amount, and persons skilled in the art will be able to judge the appropriate levels and type of glass fiber needed to achieve a given result. In general, glass fibers are added in amounts of 5 to 50% by weight.
The fire retardant component of the compositions may be a halogenated fire retardant such as brominated polystyrene. Ecologically-preferred compositions, however, are halogen-free and utilize an organophosphate fire retardant. The organophosphate fire retardant component of the compositions may be any of numerous organophosphorus fire retardants which are known in the art. Specific examples include resorcinol diphosphate, bisphenol A diphosphate, tetraxylyl piperazine diphosphoramide, and the like, e.g. such as disclosed in U.S. Pat. Nos. 4,933,386; 4,343,732; 5,455,292 and RE 36,188 herein and herewith specifically incorporated by reference. The amount of organophosphate fire retardant is selected to achieve the desired final level of fire-retardance. Because of the synergistic effects of utilizing the organoclay additives in the compositions of the invention, the amount of organophosphate fire-retardant can be reduced, and will generally be in the range of 5 to 30% by weight.
The organoclay component comprises one or more organoclay materials. As used herein, organoclay is a layered silicate clay, derived from layered minerals, in which organic structures have been chemically incorporated. Illustrative examples of organic structures are trimethyldodecylammonium ion and N,Nxe2x80x2-didodecylimidazolium ion. Since the surfaces of clay layers, which have a lattice-like arrangement, are electrically charged, they are capable of binding organic ions. There is no limitation with respect to the layered minerals employed in this invention other than that they are capable of undergoing an ion exchange with the organic ions. The preferred organoclays are layered minerals that have undergone cation exchange with organo-cations and/or onium compounds. Illustrative of such layered minerals are the kaolinite group and the montmorillonite group. It is also within the scope of this invention to employ minerals of the illite group which can include hydromicas, phengite, brammallite, glaucomite, celadonite and the like. Often, however, the preferred layered minerals include those often referred to as 2:1 layered silicate minerals like muscovite, vermiculite, saponite, hectorite and montmorillonite, wherein montmorillonite is often preferred. The layered minerals described above may be synthetically produced. However, most often they are naturally occurring and commercially available. Organoclays of the type suitable for use in this invention are described in U.S. Pat. Nos. 5,773,502 and 5,530,052 which are incorporated herein by reference.
The mineral component may be a silicate, such as mica, or regular clay or talc.
Other additives can be included in the compositions of the invention in accordance with conventional practice in the art. For example, stabilizers such as sterically hindered phenols, organic phosphites, diazide oxalates, sterically hindered amines or amine N-oxides may be incorporated. Other exemplary additives include ZnS which functions to deactivate residual copper-based catalyst present in PPE, MgO or ZnO which function as an acid quencher to quench acid generated by the deactivation of residual catalyst, and carbon black or other colorant which functions as a pigment to color the composition.
The invention will now be further described with reference to the following, non-limiting examples.